---
id: CVE-2026-77696
title: |-
  Issue summary: SM2 signature generation uses non-constant-time arithmetic
  on secret values, forming a timing side-channel.

  Impact summary: An attacker able to measure SM2 signing times may learn
  information about the per-signature secre…
summary: |-
  Issue summary: SM2 signature generation uses non-constant-time arithmetic
  on secret values, forming a timing side-channel.

  Impact summary: An attacker able to measure SM2 signing times may learn
  information about the per-signature secre…
severity: low
cvss: 3.7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'
cwe:
  - CWE-208
vendor: OpenSSL
product: OpenSSL
affected:
  - OpenSSL >= 4.0.0 < 4.0.3
  - OpenSSL >= 3.6.0 < 3.6.5
  - OpenSSL >= 3.5.0 < 3.5.9
  - OpenSSL >= 3.4.0 < 3.4.8
  - OpenSSL >= 3.0.0 < 3.0.23
  - OpenSSL >= 1.1.1 < 1.1.1zj
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T17:17:10.343'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-77696'
references:
  - url: >-
      https://github.com/openssl/openssl/commit/1c4aed808a7aea32d2d013049c2e0d9fef164fc9
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/20b20628d39b2dcc4677194bd68c7c060fa598cb
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/419f5cb519721dceed393dbc524d79e487c72e64
    label: openssl-security@openssl.org
  - url: >-
      https://github.com/openssl/openssl/commit/6b90445a56b99a328ac1feba058abf976504f440
    label: openssl-security@openssl.org
  - url: 'https://openssl-library.org/news/secadv/20260929.txt'
    label: openssl-security@openssl.org
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-09-29T16:51:30.070097Z'
ingestedAt: '2026-09-29T16:39:33.269Z'
---

## Overview

Issue summary: SM2 signature generation uses non-constant-time arithmetic
on secret values, forming a timing side-channel.

Impact summary: An attacker able to measure SM2 signing times may learn
information about the per-signature secret nonce, which over many signatures
can, via a lattice / Hidden Number Problem attack, lead to recovery of the
private key.

CWE: CWE-208: Observable Timing Discrepancy

Description: SM2 signature generation computes the signature value using
variable-time BIGNUM operations on the secret nonce and the private key, so
the time taken to produce an SM2 signature depends on these secret values,
forming a timing side-channel.

Applications performing SM2 signature generation are affected on all
platforms.

FIPS Impact: no
SM2 is not a FIPS algorithm.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.